Small diameter riser pipe system



Dec. 30, 1969 y R. P. VINCENT 3,486,555

` SMALL DIAMETER RISER PIPE SYSTEM Filed June 25, 1968 2 Sheets-Sheet 1ATTORNEY Dec. 3o, 1969 Filed June 25, 1968 SR. P. VINCENT 3,486,555

SMALL DIAMETERRISER PIPE SYSTEM 2 Sheets-Sheet 2 f RENC R VINCEN mvmon.

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ATTORNEY United States Patent O 3,486,555 SMALL DIAMETER RISER PIPESYSTEM Renic P. Vincent, Tulsa, Okla., assignor to Pau AmericanPetroleum Corporation, Tulsa, Okla., a corporation of Delaware FiledJune 25, 1968, Ser. No. 739,723 Int. Cl. E21b 33/035, 7/12, 43/01 U.S.Cl. 166-.5 8 Claims ABSTRACT OF THE DISCLOSURE This describes Ithe useof a riser pipe which has an inside diameter only about one-half to oneinch larger than the outside diameter of the drill collar and drill pipewhich must pass therethrough. The riser pipe, when being raised orlowered, is supported by a special sub or enlarged section of drill pipewhich is connected to the lower end of the drill string just above thebit. Buckling of the riser pipe is resisted by the stiffness of thedrill pipe in tension. Means are provided to guide the lower end of theriser pipe into sealing engagement with the wellhead. Thus, notensioning device is required on the vessel. By using this system, theweight of the riser system is reduced by a factor of between 10 and 20.

This invention relates to drilling in earth formations located beneath abody of water, such as in the Gulf of Mexico, in which the drillingoperations are conducted from a floating vessel. More specifically, thisinvention relates to a method and apparatus involving a riser pipe whichextends from the ocean oor to the floating vessel located at the surfaceof the body of water. It relates to a riser pipe which is only slightlylarger than the drill pipe it passes through such that the weight of theriser pipe system is reduced, for example, by a factor of l to 20 overthat of the conventional riser pipe.

Background In recent years it has become desirable to use a oatingvessel from which to drill wells in marine locations. In such operationsthe floating -vessel is sometimes connected to a submarine well bore bya long tubular member through which drill pipe, drilling uids, etc.,pass between the vessel and the well bore. This long tubular member iscommonly referred to as a riser pipe.

A submerged well head usually includes a blowout preventer and othercontrol equipment. The control equipment is usually operated byhydraulic lines which extend from the equipment to the Vessel. However,sonic instruments can be used for operating the control equipment. Inone embodiment of the commonly used systems, the upper part of the wellhead assembly includes a ball connector which provides a flexibleconnection between the well head assembly and the riser pipe. The lowerend of the riser pipe is connected to the ball joint and is free topivot thereabout. This is commonly called a flex joint. The purpose ofthis is to permit relative pivotal movement between the riser pipe whichis subject to forces such as the ocean current and the well headassembly which is secured to the earth. Other types of flex joints arecommercially available; however, the ball and socket joint is enjoyingincreasing popularity. Although a vessel is anchored, it normally hassome vertical movement and it can rise and fall from a few feet up to20-30 feet or more. To compensate for this vertical movement, a slip ortelescopic joint is provided in the riser pipe.

In conventional riser pipes which are supported solely at the lower end,its own effective weight, that is, weight in water, causes it to be in astate of axial compression increasing from zero at the top to a maximumat the Patented Dec. 30, 1969 bottom support. When drilling in deepwater, the compressive stress in the wall of the riser pipe from thissource alone is sometimes sufficient to buckle the riser pipe, that is,to cause it to bend. To counteract this buckling effect it has become apractice to apply a tensile force to the top of the riser pipe. Specialtensioning devices are mounted on the ship and have their cablesattached to the upper end of the riser pipe but below the slip joint.These tensioning devices are commonly referred to as constant tensioningdevices so that they can maintain a constant tension on the riser pipealthough the ship may rise and fall with respect to the riser pipe.These constant tensioning devices are helpful but are also' costly andmust be maintained. A failure of the tensioning device can becatastrophic.

In ordinary drilling using conventional riser pipe systems, the riserpipe may commonly -be about 20 inches in diameter and the drill stringwhich passes therethrough is commonly about 41/2 inches in diameter. Therelatively larger diameter of the riser pipe is provided so that thedrill bit, etc., at the lower end of the drill string can pass readilythrough the riser pipe. In ordinary operations the drilling fluidcirculates down through the drill pipe, out the bit at the lower endwhere the hole is being made, up the annulus, first between the drillstring and the earth, and then between the drill string and the riserpipe. The bigger the riser pipe, the greater the stresses due tobuckling, thus the greater the tensioning force which must be applied tokeep it from buckling.

Brief description of the invention Briefly, this invention concerns animproved riser pipe in which the riser pipe is only slightly larger thanthe diameter of the drill string. The lower end of the riser pipesealingly tits and mates into an upwardly facing conical surface on thesubsea well head. A drill string extends through the riser pipe and hasan operational sub of a diameter larger than the drill string attachedthereto. The sub has an outer diameter larger than the inner diameter ofthe riser pipe and supports the riser pipe when the riser pipe is beingrun into or removed from its operating position. Buckling of the riserpipe is prevented lby having either heavy drill collars extendingtherethrough or when the drill pipe is in operation, the tension is thedrill pipe imputes stiffness to the riser pipe. In this system,therefore, no tensioning device is required for the riser pipe.

Various objects and a better understanding of the invention can be hadfrom the following description taken in conjunction with the drawings inwhich:

FIGURE 1 illustrates a preferred embodiment showing the riser pipeseated in the well head and extending to a drilling vessel at thesurface;

FIGURE 2 illustrates several stands of drill collars attached to aspecial sub and bit and positioned inside small diameter riser pipesection;

FIGURE 3 illustrates the next stand, after that of FIG- URE 2, ofcollars and riser assembled as used when running into the position ofFIGURE 1.

Attention is first directed to FIGURE 1 of the drawing which illustratesa conventional subsea well head including a blowout preventer stack 10having a vertical passage therethrough. The blowout preventer stack issupported by a casing 14 which is set in larger surface casing 16. Aguide base plate 18 is supported by casing 16. A long spool 12 isattached to the upper end of the blowout preventer stack. Long spool 12is somewhat greater in length than the maximum Vertical displacement ofthe vessel due to wave and tides. The purpose of this will be explainedhereinafter. Ihe upper end of long spool 12 is provided with an upwardlyfacing conical surface 20.

Show in the drawing is a riser pipe 22 which has a lower enlargedportion 24. Attached to the lower end of the riser by clamp 25 is guidearm 40 and an inverted guide funnel 26 which has a lower sealing surface28. The guide arms 40 are loosely mounted on guide posts 39 to whichguide lines 38 are connected and extend to the floating vessel 41. Thepurpose of the funnel 26 is to aid in centering the surface 28 on theconical surface 20 of the long spool 12. A seal 30 is carried by sealingsurface 28 of the riser pipe 22. It will be noted that the matingsurface 28 of the riser pipe and the upwardly facing surface 20 of thespool 12vare spherical in shape so that they can pivot with respect toeach other without losing their seal. Thus, they make up what can becalled a ex joint. This permits the upper end of the riser pipe to movelaterally with the tide without breaking contact with the spool.

Mounted within riser pipe 22 is a drill string 32. The clearance betweendrill string 32 and riser pipe 22 is very small, being not over aboutone inch, for example. This clearance is kept small so that thestiffness of drill pipe 32 will be imputed into riser pipe 22 andprevent it from buckling. The upper end of riser pipe 22 is supported atthe upper end from ship 41 by lines 23 and a conventional slip joint 27of suitable size. No special tensioning means need be connected to lines23. It has been determined that the stiffness of the drill pipe 32 heldin tension by the weight of pipe and drill collars suspended below theriser is sucient to prevent buckling of the riser. The inherentstiffness of the drill collars is suicient to prevent buckling of theriser as it is lowered in the well.

I will now consider the manner of supporting the riser by the drillstring 32 when the riser pipe is either being run or removed. This isaccomplished by having a special sub 34 attached to the lower end ofdrill pipe 32 just above bit 36. Sub 34 is of a larger outside diameterthan the inside diameter of riser 22. Sub 34 has an upwardly facingshoulder 33 which mates with or engages the downwardly facing shoulder21 at the lower end of riser 22.

The length of spool 12 should be somewhat greater than maximum verticaldisplacement of the vessel due to wave and tide. It will be noted thatthe weight of the riser pipe 22 forces the surface 28 of funnel 26downwardly against upwardly facing surface 20 to form a good seal. Thisseal is broken when sub 34 forces the riser pipe upwardly. Thus, bymaking the length of the spool greater than the maximum verticaldisplacement of the vessel, the blowout preventer 10 can be closedbefore the riser connection is broken. This is when pulling pipe. Italso functions to permit the blowout preventers to remain closed untilthe seal is made between the riser and the spool.

FIGURE 2 is a view of the riser pipe assembly including drill collars.Shown thereon are a plurality of drill collars 22A having enlarged sub34 just above bit 44. The drill collars 22A are held in place by slips46 in rotary table 48. A safety clamp 50 has been positioned about thedrill collars just above the slip. A pickup sub 52 is connected to thetop of the top of the drill collars 22A. Mounted about the drill collarsare a plurality of stands of riser pipes 54a, 54b and 54e. These standsof riser pipes are connected by suitable riser connectors 56. The lowerstand 54a of the riser pipe is enlarged at the bottom similarly as shownin FIGURE l to provide an enlarged portion 24 having guide arm 40 andguide funnel 26 connected thereto.

FIGURE 3 illustrates a string of drill pipe or drill collars 22B closelysurrounded by three stands of riser pipes 58a, SSb and 58e connected bysuitable riser connectors. A safety clamp 60 is placed about drillcollar string 22B just below the stand of riser pipe 52a.

When it is desired to run the riser pipe into the hole, the rst step isto place several stands of riser pipe such as 52a having enlargement 24at the lower end about the string of pipe just above sub 34. The variousstands of riser pipe are connected as by clamps 56. The riser pipe isstripped down over the drill string while the pipe is still in thederrick supported above the working deck. The whole device is thenpicked up by the hoisting means on rig 60 and lowered down through slips46 which are in their open position. As soon as the lower end of riserpipe section 54a is clear below the rotary table, guide arms 40 andguide funnel 26 are connected thereto by clamp 25. The whole assembly islowered to the position shown in FIGURE 2. The slips are then set asillustrated.

At this time another set of `drill collars 22B such as shown in FIGURE 3mounted in riser section 58a, 5817 and 58C is supported in the derrick60. Safety clamp 62 mounted on drill collar 22B some distance suicientto allow tongs to be used on the drill collar below the clamps preventsthe riser pipe 58a from falling down over the lower end of drill collar26B of FIGURE 3. The drill collar is picked up by pickup sub 52 which isnow on the top of drill collar section 22B. The drill collar and riserof FIGURE 3 are then lowered and the threads 68 of drill collar 22B areconnected into the threads of the upper section of the drill collars ofFIGURE 2. At this point the riser section 58a, etc., is picked up by acatline or other auxiliary means, not specifically shown, and supportedfrom derrick 60. Safety clamp 62 is removed and the riser section islowered so that riser section 58a can be clamped or connected to theupper end of previously installed riser pipe section 54C. Additionalstands of riser pipe and drill collars are added until the riser pipehas reached the desired length so that it can rest and seat on seat 20.

A brief discussion of the procedure of removing the riser pipe assemblywill now be made. The drill pipe is removed by the use of derrick 60 ina conventional manner until the sub 34 is raised to the positionillustrated in FIGURE 2. Pickup sub 52 is placed on the upper en d ofthe drill collars, the slips 46 released and the entire assembly ofFIGURE 2 below the table 48 is raised by the raising of the drillcollars. When the drill collars have been raised their maximum distance,such as 2 or 3 joints, the upper two or three stands of riser pipes aredisconnected from the lower stands of riser pipe. An auxiliary hoistlifts the riser stand up suiciently so that a safety clamp can be placedabout the drill collars just below the lower end of the disconnectedriser pipe section, such as safety clamp 62 of FIGURE 3. Then theauxiliary means for lifting the riser pipe is removed and the uppersection of drill collars such as 22B is disconnected from the upperportion 22A after portion 22A is firmly supported by the slips. Thesafety clamp 62 is used to support the riser pipe assembly on the standof drill collars. The remaining drill collars are now lowered so thatthe remaining riser pipe joints are below table 48. The slips 46 are nowset on the drill collars so that the drill collar joint immediatelyabove the table can be broken out. Then we have a section broken out asshown in FIG- URE 3. This can be stored on the deck. Ideally, the sub 52is of sufficient length to give greater length to the string of drillcollars for manipulating the riser pipe sections thereabout. Thisprocess is repeated until all the riser pipe assembly as desired ispulled from the hole.

While the above embodiments of the 'invention have been described withconsiderable detail, it is to be understood that various modificationsof the device can be made without departing from the scope or spirit ofthe invention.

I claim:

1. A riser pipe system for use with a well in the floor of a body ofwater which comprises:

a well head having an upwardly facing surface and a vertical passagetherethrough; a drill string having a hollow sub member connected intothe lower end portion thereof, said sub being insertable in the verticalpassage of said well head, said sub member having a larger diameter thanthe other part of said drill string;

a riser pipe surrounding said drill string, the internal diameter ofsaid riser pipe being less than the diameter of said sub member, thelower end of said riser pipe having a downwardly facing surface formating and sealing with the upwardly facing surface of said well head.

2. An apparatus as defined in claim 1, including guide means to guidesaid riser pipe and drill string downwardly to engagement with said wellhead.

3. An apparatus as defined in claim 1 in which the outside diameter ofsaid drill string is not over about one inch less than the insidediameter of said inside diameter of said riser pipe.

4. An apparatus as defined in claim 2, including a downwardly openingfunnel secured to the lower end of said riser pipe for guiding the riserpipe into engagement with the upwardly facing surface of said well head.

5. A riser pipe system as defined in claim 1 for use in a floatingvessel having a vertical movement due to waves and tide which comprises:

said well head including a hollow spool of a vertical length greaterthan the vertical movement of the oating vessel, said well head furtherincluding a blowout preventer connected to the lower end of said spool.

6. A riser pipe assembly as defined in claim 1 in which the downwardlyfacing surface of the riser pipe and the upwardly facing surface of thewell head are spherical.

7. A method of removing a riser from engagement with a well head inwhich the riser is made up of at least two joints clamped together, adrill string inside said riser and having a sub of larger diameter thanthe inner diameter of said riser pipe, which comprises:

pulling up on said drill string until said sub engages the lower end ofsaid riser pipe, continue pulling on said drill string until at leastone joint of said riser pipe has cleared the work deck on said ship;

disconnecting the said first joint from said second joint;

securing the disconnected joint of the riser pipe;

lower the drill pipe and the lower section of riser pipe so that the topof the lower section of riser pipe is below the work deck;

then secure the drill collar to the work deck;

disconnect the joint of drill pipe above where it is secured;

store the disconnected joint of drill pipe and riser pipe. 8. A methodof running riser pipe from engagement with the Well head in which theriser is made up of at least two joints clamped together, drill stringinside said riser and having a hollow sub at the lower end thereof oflarger diameter than the inner diameter of said riser pipe whichcomprises:

stripping at least one joint of riser pipe down over a section of drillstring until the lower end of the riser pipe presses on said sub;lowering the drill pipe and riser down through the rotary table; placinganother section of riser pipe over another section of drill string;placing a safety clamp about the lower end of said second section ofdrill pipe to support the riser pipe section; connecting the secondsection of drill pipe to the first section supported in said rotarytable; lifting up on said second section of drill pipe; independentlylift up on said second section of riser pipe until the weight is removedfrom said clamp on said second section of drill pipe; removing saidsafety clamp; independently lowering said second section of riser pipe;clamping said second section of riser pipe to said first section;thereafter lowering said connected sections of drill pipe and saidconnected sections of said riser pipe; repeating the above steps untilsaid riser pipe engages said well head.

References Cited UNITED STATES PATENTS 3,145,775 9/ 1964 McCarty 166-.53,247,914 4/1966 Slack 166-.5 X 3,319,726 5/1967 Brown 166-.5 X3,338,303 8/1967 Hoch et al 166-.5 3,340,928 9/1967 Brown 166-.53,369,599 2/1968 Evans 166-.5 3,422,889 1/ 1969 Yost 166-.5

JAMES A. LEPPINK, Primary Examiner R. E. FAVREAU, Assistant-ExaminerU.S. Cl. X.R. -7

